Non-Orthogonal Target and Method for Using the Same in Measuring Misregistration of Semiconductor Devices

ABSTRACT

A target for use in the measurement of misregistration between layers formed on a wafer in the manufacture of semiconductor devices, the target including a first pair of periodic structures (FPPS) and a second pair of periodic structures (SPPS), each of the FPPS and the SPPS including a first edge, a second edge, a plurality of first periodic structures formed in a first area as part of a first layer and having a first pitch along a first pitch axis, the first pitch axis not being parallel to either of the first edge or second edge, and a plurality of second periodic structures formed in a second area as part of a second layer and having the first pitch along a second pitch axis, the second pitch axis being generally parallel to the first pitch axis.

REFERENCE TO RELATED APPLICATIONS

Reference is hereby made to U.S. Provisional Patent Application Ser. No.62/971,800, filed Feb. 7, 2020 and entitled PYTHAGORAS OVL METROLOGYTARGET DESIGN FOR SMALL TARGETS AND INCORPORATION OF SEM TARGET WITHOPTICAL TARGET and to U.S. Provisional Patent Application Ser. No.62/978,253, filed Feb. 18, 2020 and entitled PYTHAGORAS OVL METROLOGYTARGET DESIGN FOR SMALL TARGETS AND INCORPORATION OF SEM TARGET WITHOPTICAL TARGET, the disclosures of which are hereby incorporated byreference and priorities of which are hereby claimed.

Reference is also made to the following patents and patent applicationsof the Applicant, which are related to the subject matter of the presentapplication, the disclosures of which are hereby incorporated byreference:

-   U.S. Pat. No. 7,608,468 entitled APPARATUS AND METHODS FOR    DETERMINING OVERLAY AND USES OF SAME;-   U.S. Pat. No. 9,476,698 entitled PERIODIC PATTERNS AND TECHNIQUE TO    CONTROL MISALIGNMENT BETWEEN TWO LAYERS; and-   U.S. Pat. No. 8,330,281 entitled OVERLAY MARKS, METHODS OF OVERLAY    MARK DESIGN AND METHODS OF OVERLAY MEASUREMENTS.

FIELD OF THE INVENTION

The present invention relates to measurement of misregistration in themanufacture of semiconductor devices generally.

BACKGROUND OF THE INVENTION

Various methods and systems are known for measurement of misregistrationin the manufacture of semiconductor devices.

SUMMARY OF THE INVENTION

The present invention seeks to provide improved methods and systems formeasurement of misregistration in the manufacture of semiconductordevices.

There is thus provided in accordance with a preferred embodiment of thepresent invention a target for use in the measurement of misregistrationbetween at least one first layer and at least one second layer formed ona wafer in the manufacture of semiconductor devices, the targetincluding a first pair of periodic structures (IPPS) and a second pairof periodic structures (SPPS), each of the FPPS and the SPPS including afirst edge axis being generally parallel to a first FPPS edge, a secondedge axis being generally parallel to a second FPPS edge, a plurality offirst periodic structures formed in a first area as part of a first FPPSlayer of the at least one first layer and having a first pitch along afirst pitch axis, the first pitch axis not being parallel to either ofthe first edge axis or second edge axis, and a plurality of secondperiodic structures formed in a second area as part of a second FPPSlayer of the at least one second layer and having the first pitch alonga second pitch axis, the second pitch axis being generally parallel tothe first pitch axis and the first area and the second area at leastpartially overlying one another.

In accordance with a preferred embodiment of the present invention, thetarget also includes a third pair of periodic structures (TPPS) and afourth pair of periodic structures (FoPPS), each of the TPPS and theFoPPS including a third edge axis being generally parallel to a firstTPPS edge, a fourth edge axis being generally parallel to a second TPPSedge, a plurality of third periodic structures formed in a third area aspart of a first TPPS layer of the at least one first layer and having asecond pitch along a third pitch axis, the third pitch axis not beingparallel to either of the third edge axis or fourth edge axis, and aplurality of fourth periodic structures formed in a fourth area as partof a second TPPS layer of the at least one second layer and having thesecond pitch along a fourth pitch axis, the fourth pitch axis beinggenerally parallel to the third pitch axis and the third area, and thefourth area at least partially overlying one another.

In accordance with a preferred embodiment of the present invention, thefirst FPPS layer and the first TPPS layer are the same layer and thesecond FPPS layer and the second TPPS layer are the same layer.Alternatively, in accordance with a preferred embodiment of the presentinvention, at least one of the first FPPS layer and the first TPPS layerare different layers and the second FPPS layer and the second IPPS layerare different layers.

Preferably, the third pitch axis is generally perpendicular to the firstpitch axis. Preferably, the first pitch axis forms a generally 45° anglewith the first edge axis. Preferably, the second edge axis is generallyperpendicular to the first edge axis.

In accordance with a preferred embodiment of the present invention,portions of the semiconductor devices are generally parallel to a firstsemiconductor device axis and the first pitch, axis is generallyperpendicular to the first semiconductor device axis. Preferably, thetarget also, includes electron beam sensible portions including aplurality of first features formed as part of the at least one firstlayer of the wafer and a plurality of second features formed as part ofthe at least one second layer of the wafer. In a preferred embodiment ofthe present invention, the FPPS, the SPPS and the electron beam sensibleportions are all formed in a single target-dedicated region on thewafer. Preferably, the target is rotationally symmetric about a singlepoint of symmetry.

Alternatively, in accordance with a preferred embodiment of the presentinvention, portions of the semiconductor devices are generally parallelto a first semiconductor axis, and the first pitch axis is notperpendicular to the first semiconductor device axis. In accordance witha preferred embodiment of the present invention, first pitch axis formsa generally 45° angle with the first semiconductor device axis.Alternatively, in accordance with a preferred embodiment of the presentinvention, the target has a first size and is formed in atarget-dedicated region, the target-dedicated region having a secondsize, and the target is oriented within the target-dedicated region suchthat the ratio of the first size to the second size is generallymaximized.

Preferably, the first pitch axis, the first edge axis and the secondedge axis are arranged such that when either of the FPPS or the SPPS isilluminated by light, there results a desired output signal along asignal axis, the signal axis not being perpendicular to either of thefirst edge axis or the second edge axis, and a noise output signal alonga first noise axis and a second noise axis, the first noise axis beinggenerally perpendicular to the first edge axis and the second noise axisbeing generally perpendicular to the second edge axis. Preferably,overlap between the noise output signal and the desired output signal isgenerally minimized.

There is also provided in accordance with another preferred embodimentof the present invention a method of measuring misregistration betweenat least one first layer and at least one second layer formed on a waferin the manufacture of semiconductor devices, the method includingproviding the wafer on which is formed a target including a first pairof periodic structures (FPPS) and a second pair of periodic structures(SPPS), each of the FPPS and the SPPS including a first edge, axis beinggenerally parallel to a first FPPS edge, a second edge axis beinggenerally parallel to a second FPPS edge, a plurality of first periodicstructures formed in a first area as part of a first FPPS layer of theat least one first layer and having a first pitch along a first pitchaxis, the first pitch axis not being parallel to either of the firstedge axis or second edge axis, and a plurality of second periodicstructures formed in a second area as part of a second FPPS layer of theat least one second layer and having the first pitch along a secondpitch axis, the second pitch axis being generally parallel to the firstpitch axis and the first area and the second area at least partiallyoverlying one another, illuminating the target with incident radiation,thereby generating output signals and analyzing the output signal,thereby generating a misregistration value between the layers of thetarget.

Preferably, the output signal includes a desired output signal along asignal axis, the signal axis not being perpendicular to either of thefirst edge axis or the second edge axis; and a noise output signal alonga first noise axis and a second noise axis, the first noise axis beinggenerally perpendicular to the first edge axis and the second noise axisbeing generally perpendicular to the second edge axis. Preferably,overlap between the noise output signal and the desired output signal isgenerally minimized.

In a preferred embodiment of the present invention, the analyzing theoutput signal includes identifying and removing the noise output signalof the output signal. In a preferred embodiment of the presentinvention, the output signal is generated by a scatterometrymisregistration metrology tool.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1A is a simplified generally top planar illustration of oneembodiment of a target of the present invention;

FIGS. 1B, 1C, 1D and 1E are simplified cross-sectional illustrations ofthe target shown in FIG. 1A, being taken along respective lines B-B,C-C, D-D and E-E in FIG. 1A;

FIGS. 1F and 1G are simplified top planar illustrations of a first layerand a second layer of the target shown in FIGS. 1A-1E, respectively;

FIG. 2A is a simplified illustration of an output signal generated by aportion of the target shown in FIGS. 1A-1G when suitably illuminated;

FIG. 2B is a simplified illustration of an output signal generated by aportion of a prior art target when suitably illuminated;

FIG. 3A is a simplified generally top planar illustration of a preferredembodiment of a target of the present invention;

FIGS. 3B, 3C, 3D and 3E are simplified cross-sectional illustrations ofthe target shown in FIG. 3A, being taken along respective lines B-B,C-C, D-D and E-E in FIG. 3A;

FIGS. 3F and 3G are simplified top planar illustrations of a first layerand a second layer of the target shown in FIGS. 3A-3E, respectively;

FIG. 4 is a simplified illustration of an output signal generated by aportion of the target shown in FIGS. 3A-3G when suitably illuminated;and

FIG. 5 is a simplified generally top planar illustration of anotherpreferred embodiment of a target of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The targets of the present invention, described hereinbelow withreference to FIGS. 1A-5, are preferably used in a system and method tomeasure misregistration between at least a first layer and a secondlayer of semiconductor device structures formed on a wafer and aretypically formed as part of a manufacturing process for semiconductordevices. The misregistration measured by the system and method describedhereinbelow with reference to FIGS. 1A-5 may be used to adjust portionsof the manufacturing process for semiconductor devices, such aslithography, to ameliorate misregistration between various layers of thesemiconductor devices being fabricated.

The targets described hereinbelow with reference to FIGS. 1A-5 includeperiodic indicia formed as part of at least the first layer and thesecond layer formed on the wafer, preferably during the formation of thesemiconductor devices on the wafer. The periodic indicia preferably havea pitch of 70 nm-2000 nm, and more preferably of 300 nm-700 nm, and aline width of 10%-90% of the pitch, most typically 50% of the pitch.Each of the periodic indicia may be segmented, though they need not be.In an embodiment, wherein the periodic indicia are segmented, each oneof the periodic indicia is defined by a plurality of periodicsub-indicia. Preferably, the pitch of the periodic sub-indicia is thesame as or close to the dimension of functional features of thesemiconductor devices on the wafer on which the targets are formed, butit need not be.

For example, periodic indicia having a width of 420 nm may be formed of15 periodic sub-indicia each having a pitch of 14 nm. The layers withwhich the target is formed may be mutually adjacent layers but need notbe, and may be separated by a height ranging from 50 nm to over 10,000nm. The first layer may be formed below the second layer or the secondlayer may be formed below the first layer. In some embodiments of thepresent invention, the first layer and the second layer may be the samelayer. Any material between a suitable misregistration tool radiationsource and each of the layers is at least partially transparent toradiation generated by the radiation source.

It is further appreciated that although the targets of the presentinvention are shown in FIGS. 1A-5 as being generally square in shape,the targets may be of any suitable shape. Additionally, the targets ofthe present invention may be formed in arrays, preferably in such a waythat the targets fill a maximum amount of space on the wafer that isallotted for the formation of targets useful in misregistrationmeasurement.

The present invention seeks to provide a target and a method of usethereof, which improve a signal-to-noise ratio (SNR) of amisregistration measurement output signal. More particularly, asdescribed hereinbelow, the SNR is sought to be improved by forming thetarget in such a way that noise generated by edges of the target duringmisregistration measurement propagates in a direction such that overlapbetween the noise and a desired portion of the output signal isgenerally minimized.

Reference is now made to FIG. 1A, which is a simplified generally topplanar illustration of one embodiment, of a target of the presentinvention, formed OD a wafer, to FIGS. 1B-1E, which are simplifiedcross-sectional illustrations of the target shown in FIG. 1A, and toFIGS. 1F and 1G, which are simplified top planar illustrations of afirst layer and a second layer of the target shown in FIGS. 1A-1E,respectively.

As seen in FIGS. 1A-1G, formed on a wafer 100 are at least a first layer102 and a second layer 104. Preferably, first layer 102 and second layer104 include, inter alia, semiconductor device features (not shown),portions of which are generally parallel to either of a semiconductordevice axis 106 and semiconductor device axis 108. In FIG. 1A,semiconductor device axis 106 and semiconductor device axis 108 areshown as perpendicular to each other, but they need not be.

It is appreciated that, for ease of understanding, FIGS. 1A-1G are notdrawn to scale. It is further appreciated that in a preferred embodimentof the present invention, at least some features shown may be, andtypically are, covered by other structures also formed on the wafer.

As seen particularly in FIG. 1A, in one embodiment of the presentinvention, a target 110 is formed within a target-dedicated region 111on wafer 100. Typically, the sides of target-dedicated region 111 aregenerally parallel to one or both of semiconductor device axes 106 and108. In a preferred embodiment of the present invention, the size andorientation of target 110 is chosen to generally maximize the ratio ofthe size of target 110 to the size of target-dedicated region 111.Target 110 preferably includes a first pair of periodic structures(FPPS) 112, a second pair of periodic structures (SPPS) 114, a thirdpair of periodic structures (IPPS) 116 and a fourth pair of periodicstructures (FoPPS) 118.

Each of FPPS 112 and SPPS 114 includes a pair of first edges 122 and apair of second edges 124. Preferably, first edges 122 are generallyparallel to a first edge axis 126, and second edges 124 are generallyparallel to a second edge axis 128. In the embodiment shown in FIGS.1A-1G, first edge axis 126 and second edge axis 128 are generallyperpendicular to each other, first edge axis 126 being parallel to anx-axis and second edge axis 128 being parallel to a y-axis. In otherembodiments of the present invention, first edge axis 126 and secondedge axis 128 are not perpendicular to one another. In one embodiment ofthe present invention, edge axes 126 and 128 are generally parallel tocorresponding semiconductor device axes 106 and 108, respectively.

As seen particularly in FIGS. 1F & 1G, periodic structures of each ofFPPS 112 and SPPS 114 are preferably periodic along a first pitch axis132, which is parallel to an x′-axis, and suitable measurement of FPPS112 and SPPS 114 provides output signals relating to the misregistrationbetween first layer 102 and second layer 104 in the x′ direction. Asseen particularly in FIG. 1A, FPPS 112 and SPPS 114 together form an x′target portion 134. It is a particular feature of the present inventionthat first pitch axis 132 is not parallel to either of first, edge axis126 or second edge axis 128. In a preferred embodiment of the presentinvention, first pitch axis 132 forms a generally 45° angle with one orboth of first edge axis 126 and second edge axis 128.

Similarly, each of TPPS 116 and FoPPS 118 includes a pair of first edges142 and a pair of second edges 144. Preferably, first edges 142 aregenerally parallel to a first edge axis 146, and second edges 144 aregenerally parallel to a second edge axis 148. In the embodiment shown inFIGS. 1A-1G, first edge axis 146 and second edge axis 148 are generallyperpendicular to each other, first edge axis 146 being parallel to anx-axis and second edge axis 148 being parallel to a y-axis. In otherembodiments of the present invention, first edge axis 146 and secondedge axis 148 are not perpendicular to one another. In one embodiment ofthe present invention, edge axes 146 and 148 are generally parallel tocorresponding semiconductor device axes 106 and 108, respectively.

As seen particularly in FIGS. 1F & 1G, periodic structures of each ofTPPS 116 and FoPPS 118 are preferably periodic along a second pitch axis152, which is parallel to a y′-axis, and suitable measurement of TPPS116 and FoPPS 118 provides output signals relating to themisregistration between first layer 102 and second layer 104 in the y′direction. As seen particularly in FIG. 1A, TPPS 116 and FoPPS 118together form a y′ target portion 154. It is a particular feature of thepresent invention that second pitch axis 152 is, not parallel to eitherof first edge axis 126 or second edge axis 128. In a preferredembodiment of the present invention, second pitch axis 152 forms agenerally 45° angle with one or both of first edge axis 126 and secondedge axis 128.

As seen, in FIGS. 1B-1G, FPPS 112 preferably includes a plurality offirst periodic structures 162 formed as part of first layer 102 and aplurality of second periodic structures 164 formed as part of secondlayer 104. Preferably, SPPS 114 includes a plurality of first periodicstructures 166 formed as part of first layer 102 and a plurality ofsecond periodic structures 168 formed as part of second layer 104.Preferably, the area of FPPS 112 in which first periodic structures 162are formed and the area of FPPS 112 in which second periodic structures164 are formed at least partially overlie one another. Similarly, thearea of SPPS 114 in which first periodic structures 166 are formed andthe area of SPPS 114 in which second periodic structures 168 are formedat least partially overlie one another.

Preferably, periodic structures 162 and 164 are characterized by apitch, K, along first pitch axis 132 and periodic structures 166 and 168are characterized by a pitch, L, along first pitch axis 132. In apreferred embodiment of the present invention, pitch K and pitch L havethe same value. Preferably, as seen particularly in FIG. 1B, secondperiodic structures 164 are shifted by a predetermined distance in thex′ direction with respect to first periodic structures 162. The size anddirection of the shift between first periodic structures 162 and secondperiodic structures 164 is expressed as a first predetermined offset(FPO), f₁. FPO f₁ is characterized by a first direction along an axisparallel to the x′-axis and a first magnitude. FPO f₁ preferably has amagnitude of 10 nm-100 nm, and more preferably of 15 nm-25 nm.

It is appreciated that, as described hereinabove, the magnitude anddirection of FPO f₁ characterize the shift between first periodicstructures 162 and second periodic structures 164 when target 110 is ina state of perfect registration. In a typical case, whereinmisregistration between layers 102 and 104 is not equal to zero, theactual shift between first periodic structures 162 and second periodicstructures 164 is equal to the vector sum of FPO f₁ and themisregistration.

Similarly, as seen particularly in FIG. 1C, second periodic structures168 are shifted by a predetermined distance in the x′ direction withrespect to first periodic structures 166. The size and direction of theshift between first periodic structures 166 and second periodicstructures 168 is expressed as a second predetermined offset (SPO), f₂.SPO f₂ is characterized by a second direction along an axis parallel tothe x′-axis and a second magnitude. SPO f₂ preferably has a magnitude of10 nm-100 nm, and more preferably of 15 nm-25 nm. In a preferredembodiment of the present invention, the magnitude of SPO f₂ has thesame value as the magnitude of FPO f₁, and the direction of SPO f₂ isopposite the direction of FPO f₁.

It is appreciated that, as described hereinabove, the magnitude anddirection of SPO f₂ characterize the shift between first periodicstructures 166 and second periodic structures 168 when target 110 is ina state of perfect registration. Ina typical case, whereinmisregistration between layers 102 and 104 is not equal to zero, theactual shift between first periodic structures 166 and second periodicstructures 168 is equal to the vector sum of SPO f₂, and themisregistration.

As seen particularly in FIGS. 1D & 1E, TPPS 116 preferably includes aplurality of first periodic structures 172 formed as part of first layer102 and a plurality of second periodic structures 174 formed as part ofsecond layer 104. Preferably, FoFPS 118 includes a plurality of firstperiodic structures 176 formed as part of first layer 102 and aplurality of second periodic structures 178 formed as part of secondlayer 104.

In another embodiment of the present invention, x′ target portion 134may be used in the measurement of misregistration between a first pairof layers formed on wafer 100, and y′ target portion 154 may be used inthe measurement of misregistration between a different pair of layersformed on wafer 100. In one such embodiment, periodic structures 162,164, 166 and 168 of x′ target portion 134 are formed as part of layers102 and 104, while periodic structures 172, 174, 176 and 178 of y′target portion 154 are formed as part of layers on wafer 100 other thanlayer 102 and layer 104. In another such embodiment, periodic structures162, 164, 166 and 168 of x′ target portion 134 are formed as part oflayers 102 and 104, while some of periodic structures 172, 174, 176 and178 of y′ target portion 154 are formed as part of one of layers 102 and104, while the rest of periodic structures 172, 174, 176 and 178 areformed as part of a layer on wafer 100 that is neither layer 102 norlayer 104.

Preferably, the area of TPPS 116 in which first periodic structures 172are formed and the area of TPPS 116 in which second periodic structures174 are formed at least partially overlie one another. Similarly, thearea of FoPPS 118 in which first, periodic structures 176 are formed andthe area of FoPPS 118 in which second periodic structures 178 are formedat least partially overlie one another.

Preferably, periodic structures 172 and 174 are characterized by apitch, M, along second pitch axis 152 and periodic structures 176 and178 are characterized by a pitch, N, along second pitch axis 152. In apreferred embodiment of the present invention, pitch M and pitch N havethe same value. In other embodiments of the present invention, any orall of pitches K, L, M and N have the same values. Preferably, as seenparticularly in FIG. 1D, second periodic structures 174 are shifted by apredetermined distance in the y′ direction with respect to firstperiodic structures 172. The size and direction of the shift betweenfirst periodic structures 172 and second periodic structures 174 isexpressed as a third predetermined offset (TPO), f₃. TPO f₃ ischaracterized by a first direction along an axis parallel to the y′-axisand a third magnitude. TPO f₃ preferably has a magnitude of 10 nm-100nm, and more preferably of 15 nm-25 nm.

It is appreciated that, as described hereinabove, the magnitude anddirection of TPO f₃ characterize the shift between first periodicstructures 172 and second periodic structures 174 when target 110 is ina state of perfect registration. In a typical case,wherein-misregistration between layers 102 and 104 is not equal to zero,the actual shift between first, periodic structures 172 and secondperiodic structures 174 is equal to the vector sum of TPO 6 and themisregistration.

Similarly, as seen particularly in FIG. 1E, second periodic structures178 are shifted by a predetermined distance in the y′ direction withrespect to first periodic structures 176. The size and direction of theshift between first periodic structures 176 and second periodicstructures 178 is expressed as a fourth predetermined offset (FoPO), f₄.FoPO f₄ is characterized by a second direction along an axis parallel tothe y′-axis and a fourth magnitude. FoPO f₄ preferably has a magnitudeof 10 nm-100 nm, and more preferably of 15 nm-25 nm. In a preferredembodiment of the present invention, the magnitude of FoPO f₄ has thesame value as the magnitude of TPO f₃, and the direction of FoPO f₄ isopposite the direction of TPO f₃.

It is appreciated that, as described hereinabove, the magnitude anddirection of FoPO f₄ characterize the shift between first periodicstructures 176 and second periodic structures 178 when target 110 is ina state of perfect registration. In a typical case, whereinmisregistration between layers 102 and 104 is not equal to zero, theactual shift between first periodic structures 176 and second periodicstructures 178 is equal to the vector sum of FoPO f₄ and themisregistration.

In the embodiment shown in FIGS. 1A-1G, as seen particularly in FIG. 1B,individual periodic structures of first periodic structures 162 andsecond periodic structures 164 fully or partially overlie each other. Inanother embodiment of the present invention, although the areas in whichfirst periodic structures 162 and second periodic structures 164 areformed overlie each other, the chosen line widths of first periodicstructures 162, line widths of second periodic structures 164, pitch K,pitch L, FPO f₁ and SPO f₂ may result in individual periodic structuresof first periodic structures 162 and second periodic structures 164alternating in the x′ direction with no overlap between individualperiodic structures. Similarly, in another embodiment of the presentinvention, the chosen line widths of first periodic structures 162, linewidths of second periodic structures 164, pitch K, pitch L, FPO f₁ andSPO f₂ may result in some of individual periodic structures of firstperiodic structures 162 and second periodic structures 164 fully orpartially overlying each other, and some of individual periodicstructures of first periodic structures 162 and second periodicstructures 164 alternating in the x′ direction with each other.

Similarly, individual periodic structures of first periodic structures166 and second periodic structures 168, first periodic structures 172and second periodic structures 174, and first periodic structures 176and second periodic structures 178 may either overlie or alternate witheach other.

It is appreciated that although target 110, as in the embodiment shownin FIGS. 1A-1G and described hereinabove, includes both x′ targetportion 134 and y′ target portion 154, in another embodiment of thepresent invention, target 110 may include only one of x′ target portion134 and y′ target portion 154. Such a target is useful in themeasurement of misregistration between layers 102 and 104 in the x′direction or y′ direction, respectively.

Reference is now additionally made to FIG. 2A, which is a simplifiedillustration of an output signal generated by a portion of target 110when suitably illuminated, and to FIG. 2B, which is a simplifiedillustration of an output signal generated by a portion of a prior arttarget when suitably illuminated. It is appreciated that FIGS. 2A and 2Bare illustrative in nature, and are not drawn to scale.

As seen in FIG. 2A, an x′ target cell 202, being one of FPPS 112 or SPPS114, generates an output signal 210 upon suitable illumination andmeasurement by a scatterometry misregistration metrology tool. Anexample of a scatterometry misregistration metrology tool useful in themeasurement of target 110 is an ATL™ 100, commercially available fromKLA Corporation of Milpitas, Calif., USA.

Output signal 210 typically includes a desired signal portion 212,generated by positive first-order diffraction of incident radiation, byx′ target cell 202, and a desired signal portion 214, generated bynegative first-order diffraction of incident radiation by x′ target cell202.

As is known in the art and described in further detail in U.S. Pat. Nos.9,476,698, 8,330,281 and M. Adel, D. Kandel, V. Levinski, J. Seligson,A. Kuniaysky, “Diffraction order control in overlay metrology: a reviewof the roadmap options,” Proc. SPIE 6922, Metrology, Inspection, andProcess Control for Microlithography XXII, 692202 (14 Mar. 2008), adifference between desired signal portion 212 and desired signal portion214 is a function of misregistration in the x′ direction between layers102 and 104, and misregistration between layers 102 and 104 in the x′direction may be calculated from output signal 210.

Output signal 210 typically further includes a signal portion 216,generated by 0^(th)-order diffraction of incident radiation by x′ targetcell 202. Associated with each of signal portions 212, 214 and 216 are aplurality of noise portions 230. Noise portions 230 include noiseportions 232, which are generated by diffraction of incident radiationby edges of 122 x′ target cell 202, and noise portions 234, which aregenerated by diffraction of incident radiation by edges 124 of x′ targetcell 202.

As is known in the art, as with all similar structures, edges 122 and124 of x′ target cell 202 diffract incident radiation in a directiongenerally perpendicular to respective edge axes 126 and 128. Thus, noiseportions 232 of output signal 210 propagate generally along a noise axisgenerally perpendicular to edge axis 126 and noise portions 234propagate generally along a noise axis generally perpendicular to edgeaxis 128. As is known in the art, as with all similar periodicstructures, FPPS 112 and SPAS 114 each diffract incident radiation in adirection generally parallel to pitch axis 132. Thus, desired signalportions 212 and 214 of output signal 210 are located along an axis 242,being generally parallel to corresponding pitch axis 132.

Since pitch axis 132 is not perpendicular to either of edge axes 126 or128, when illuminating x′ target cell 202 of target 110 of the presentinvention with suitable incident radiation, the axes along which noiseportions 230, generated by diffraction of incident radiation by edges122 and 124, propagate are not parallel to axis 242 along which desiredsignal portions 212 and 214, diffracted by x′ target cell 202,propagate. Thus, as seen in FIG. 2A, the undesired contributions ofnoise portions 230 to output signal 210 of target 110 can be readilyidentified and removed, thereby improving the SNR of output signal 210.

In a most preferred embodiment of the present invention, in which pitchaxis 132 forms a generally 45° angle with both of edge axes 126 and 128,the axes along which noise portions 230 propagate are located at amaximum possible planar radial distance from axis 242 along whichdesired signal portions 212 and 214, diffracted by FPPS 112 and SPPS114, propagate. Thus, the undesired contributions of noise portions 230to output signal 210 can be readily identified and removed, therebyimproving the SNR of output signal 210.

In contrast, as seen in FIG. 2B, in prior art targets useful in themeasurement of misregistration between layers formed on a wafer ofsemiconductor devices, the targets include a plurality of target cells250, which are each formed with pairs of edges 252 and 254. Target cells250 typically include periodic structures 262 and 264, which aregenerally periodic along a pitch axis 272, pitch axis 272 beinggenerally perpendicular to one of pairs of edges 252 and 254. In theembodiment of the prior art target cell shown in FIG. 2B, pitch axis 272is generally perpendicular to edges 252.

Upon measurement by a suitable scatterometry misregistration measurementtool, target cell 250 generates a signal 280. Signal 280 typicallyincludes desired signal portions 282 and 284, 0^(th)-order diffractionof incident radiation signal portion 286, noise portions 292, which aregenerated by diffraction of incident radiation by edges 252 of targetcell 250, and noise portions 294, which are generated by diffraction ofincident radiation by edges 254 of target cell 250.

Since pitch axis 272 is generally perpendicular to edges 252, both noiseportions 292 and desired signal portions 282 tend to propagate along asingle axis 296. Thus, the undesired contributions of noise 292 tooutput signal 280 cannot be readily identified and removed, and thus,output signal 280 has a lower SNR than the SNR of the targets of thepresent invention.

It is appreciated that while FIG. 2A shows output signal 210 for only asingle one of FPPS 112 or SPPS 114, typically both of FPPS 112 and SPPS114 are measured, and output signals 210 from both of FPPS 112 and SPPS114 are analyzed in order to determine both a magnitude and a directionof misregistration in the x′ direction between layers 102 and 104.

It is appreciated that upon suitable illumination and measurement ofeach of TPPS 116 and FoPPS 118 by a scatterometry misregistrationmeasurement tool, an output signal, similar to output signal 210described hereinabove with reference to FIG. 2A, is generated.Typically, the output signal generated by each of TPPS 116 and FoPPS 118is qualitatively identical, to an output signal 210 that has beenrotated such that axis 242 is parallel to pitch axis 152. Thus,misregistration in the y′ direction between layers 102 and 104 may becalculated from the output signals generated by TPPS 116 and FoPPS 118.

More particularly, each of the output signals generated by TPPS 116 orFoPPS 118 includes desired signal portions of the output signal similarto desired signal portions 212 and 214, which are located along an axisbeing generally parallel to corresponding pitch axis 152. Typically,each of the output signals generated by TPPS 116 or FoPPS 118 furtherinclude noise portions, similar to noise portions 230, which propagatein a different direction than that of axis 152.

Reference is now made to FIG. 3A, which is a simplified generally topplanar illustration of a preferred embodiment of a target of the presentinvention, formed on a wafer, to FIGS. 3B-3E, which are simplifiedcross-sectional illustrations of the target shown in FIG. 3A, and toFIGS. 3F and 3G, which are simplified top planar illustrations of afirst layer and a second layer of the target shown in FIGS. 3A-3E,respectively.

As seen in FIGS. 3A-3G, formed on a wafer 300 are at least a first layer302 and a second layer 304. Preferably, first layer 302 and second layer304 include, inter alia, semiconductor device features (not shown),portions of which are generally parallel to either of a semiconductordevice axis 306 and semiconductor device axis 308. In FIG. 3A,semiconductor device axis 306 and semiconductor device axis 308 areshown as perpendicular to each other, but they need not be.

It is appreciated that, for ease of understanding, FIGS. 3A-3G are notdrawn to scale. It is further appreciated that in a preferred embodimentof the present invention, at least some features shown may be, andtypically are, covered by other structures also formed on the wafer.

As seen particularly in FIG. 3A, in one embodiment of the presentinvention, a target 310 is formed within a target-dedicated region 311on wafer 300. Typically, the sides of target-dedicated region 311 aregenerally parallel to one or both of semiconductor device axes 306 and308. In a preferred embodiment of the present invention, the size oftarget 310 is chosen to generally maximize the ratio of the size oftarget 310 to the size of target-dedicated region 311. Target 310preferably includes a first pair of periodic structures (FPPS) 312, asecond pair of periodic structures (SPPS) 314, a third pair of periodicstructures (IPPS) 316 and a fourth pair of periodic structures (FoPPS)318.

Each of FPPS 312 and SPPS 314 includes a pair of first edges 322 and apair of second edges 324. Preferably, first edges 322 are generallyparallel to a first edge axis 326, and second edges 324 are generallyparallel to a second edge axis 328. In the embodiment shown in FIGS.3A-3G, first edge axis 326 and second edge axis 328 are generallyperpendicular to each other, first edge axis 326 being parallel to anx-axis and second edge axis 328 being parallel to a y-axis. In otherembodiments of the present invention, first edge axis 326 and secondedge axis 328 are not perpendicular to one another. In a preferredembodiment of, the present invention, edge axes 326 and 328 form agenerally 45° angle with corresponding semiconductor device axes 306 and308, respectively.

As seen particularly in FIGS. 3F & 3G, periodic structures of each ofFPPS 312 and SPPS 314 are preferably periodic along a first pitch axis332, which is parallel to an x′-axis, and suitable measurement of FPPS312 and SPPS 314 provides output signals relating to the misregistrationbetween first layer 302 and second layer 304 in the x′ direction. In apreferred embodiment of the present invention, the x′ direction is thesame as the direction as that of semiconductor device axis 306. As seenparticularly in FIG. 3A, FPPS 312 and SPPS 314 together form an x′target portion 334. It is a particular feature of the present inventionthat first pitch axis 332 is not parallel to either of first edge axis326 or second edge axis 328. In a preferred embodiment of the presentinvention, first pitch axis 332 forms a generally 45° angle with one orboth of first edge axis 326 and second edge axis 328.

Similarly, each of TPPS 316 and FoPPS 318 includes a pair of first edges342 and a pair of second edges 344. Preferably, first edges 342 aregenerally parallel to a first edge axis 346, and second edges 344 aregenerally parallel to a second edge axis 348. In the embodiment shown inFIGS. 3A-3G, first edge axis 346 and second edge axis 348 are generallyperpendicular to each other, first edge axis 346 being parallel to anx-axis and second edge axis 348 being parallel to a y-axis. In otherembodiments of the present invention, first edge axis 346 and secondedge axis 348 are not perpendicular to one another. In a preferredembodiment of the present invention, edge axes 346 and 348 form agenerally 45° angle corresponding semiconductor device axes 306 and 308,respectively.

As seen particularly in FIGS. 3F & 3G, periodic structures of each ofTPPS 316 and FoPPS 318 are preferably periodic along a second pitch axis352, which is parallel to a y′-axis, and suitable measurement of TPPS316 and FoPPS 318 provides output signals relating to themisregistration between first layer 302 and second layer 304 in the y′direction. In a preferred embodiment of the present invention, the y′direction is the same as the direction as that of semiconductor deviceaxis 308. As seen particularly in FIG. 3A, TPPS 316 and FoPPS 318together form a y′ target portion 354. It is a particular feature of thepresent invention that second pitch axis 352 is not parallel to eitherof first edge axis 326 or second edge axis 328. In a preferredembodiment of the present invention, second pitch axis 352 forms agenerally 45° angle with one or both of first edge axis 326 and secondedge axis 128.

As seen in FIGS. 3B-3G, FPPS 312 preferably includes a plurality offirst periodic structures 362 formed as part of first layer 302 and aplurality of second periodic structures 364 formed as part of secondlayer 304. Preferably, SPPS 314 includes a plurality of first periodicstructures 366 formed as part of first layer 302 and a plurality ofsecond periodic structures 368 formed as part of second layer 304.Preferably, the area of FPPS 312 in which first periodic structures 362are formed and the area of FPPS 312 in which second periodic structures364 are formed at least partially overlie one another. Similarly, thearea of SPPS 314 in which first periodic structures 366 are formed andthe area of SPPS 314 in which second periodic structures 368 are formedat least partially overlie one another.

Preferably, periodic structures 362 and 364 are characterized by apitch, P, along first pitch axis 332 and periodic structures 366 and 368are characterized by a pitch, Q, along first pitch axis 332. In apreferred embodiment of the present invention, pitch P and pitch Q havethe same value. Preferably, as seen particularly in FIG. 3B, secondperiodic structures 364 are shifted by a predetermined distance in thex′ direction with respect to first periodic structures 362. The size anddirection of the shift between first periodic structures 362 and secondperiodic structures 364 is expressed as a first predetermined offset(FPO), g₁. FPO g₁ is characterized by a first direction along an axisparallel to the x′-axis and a first magnitude. FPO g₁ preferably has amagnitude of 10 nm-100 nm, and more preferably of 15 nm-25 nm.

It is appreciated that, as described hereinabove, the magnitude anddirection of FPO g₁ characterize the shift between first periodicstructures 362 and second periodic structures 364 when target 310 is ina state of perfect registration. In a typical case, whereinmisregistration between layers 302 and 304 is not equal to zero, theactual shift between first periodic structures 362 and second periodicstructures 364 is equal to the vector sum of FPO g₁ and themisregistration.

Similarly, as seen particularly in FIG. 3C, second periodic structures368 are shifted by a predetermined distance in the x′ direction withrespect to first periodic structures 366. The size and direction of theshift between first periodic structures 366 and second periodicstructures 368 is expressed as a second predetermined offset (SPO), g₂.SPO g₂ is characterized by a second direction along an axis parallel tothe x′-axis and a second magnitude. SPO g₂ preferably has a magnitude of10 nm-100 nm, and more preferably of 15 nm-25 nm. In a preferredembodiment of the present invention, the magnitude of SPO g₂ has thesame value as the magnitude of FPO g₁, and the direction of SPO g₂ isopposite the direction of FPO g₁.

It is appreciated that, as described hereinabove, the magnitude anddirection of SPO g₂ characterize the shift between first periodicstructures 366 and second periodic structures 368 when target 310 is ina state of perfect registration. In a typical case, whereinmisregistration between layers 302 and 304 is not equal to zero, theactual shift between first periodic structures 366 and second periodicstructures 368 is equal to the vector sum of SPO g₂ and themisregistration.

As seen particularly in FIGS. 3D & 3E, TPPS 316 preferably includes aplurality of first periodic structures 372 formed as part of first layer302 and a plurality of second periodic structures 374 formed as part ofsecond layer 304. Preferably, FoPPS 318 includes a plurality of firstperiodic structures 376 formed as part of first layer 302 and aplurality of second periodic structures 378 formed as part of secondlayer 304.

In another embodiment of the present invention, x′ target portion 334may be used in the measurement of misregistration between a first pairof layers formed on wafer 300, and y′ target portion 354 may be used inthe measurement of misregistration between a different pair of layersformed on wafer 300. In one such embodiment, periodic structures 362,364, 366 and 368 of x′ target portion 334 are formed as part of layers302 and 304, while periodic structures 372, 374, 376 and 378 of y′target portion 354 are formed as part of layers on wafer 300 other thanlayer 302 and layer 304. In another such embodiment periodic structures362, 364, 366 and 368 of x′ target portion 334 are formed as part oflayers 302 and 304, while some of periodic structures 372, 374, 376 and378 of y target portion 354 are formed as part of one of layers 302 and304, while the rest of periodic structures 372, 374, 376 and 378 areformed as part of a layer on wafer 300 that is neither layer 302 norlayer 304.

Preferably, the area of TPPS 316 in which first periodic structures 372are formed and the area of TPPS 316 in which second periodic structures374 are formed at least partially overlie one another. Similarly, thearea of FoPPS 318 in which first periodic structures 376 are formed andthe area of FoPPS 318 in which second periodic structures 378 are formedat least partially overlie one another.

Preferably, periodic structures 372 and 374 are characterized by apitch, R, along second pitch axis 352 and periodic structures 376 and378 are characterized by a pitch, S, along second pitch axis 352. In apreferred embodiment of the present invention, pitch R and pitch S havethe same value. In other embodiments of the present invention, any orall of pitches P, Q, R and S have the same values. Preferably, as seenparticularly in FIG. 3D, second periodic structures 374 are shifted by apredetermined distance in the y′ direction with respect to firstperiodic structures 372. The size and direction of the shift betweenfirst periodic structures 372 and second periodic structures 374 isexpressed as a third predetermined offset (TPO), g₃. TPO g₃ ischaracterized by a first direction along an axis parallel to the y′-axisand a third magnitude. TPO g₃ preferably has a magnitude of 10 nm-100nm, and more preferably of 15 nm-25 nm.

It is appreciated that, as described hereinabove, the magnitude anddirection of TPO g₃ characterize the shift between first periodicstructures 372 and second periodic structures 374 when target 310 is ina state of perfect registration. In a typical case, whereinmisregistration between layers 302 and 304 is not equal to zero, theactual shift between first, periodic structures 372 and second periodicstructures 374 is equal to the vector sum of TPO g₃ and themisregistration.

Similarly, as seen particularly in FIG. 3E, second periodic structures378 are shifted by a predetermined distance in the y′ direction withrespect to first periodic structures 376. The size and direction of theshift between first periodic structures 376 and second periodicstructures 378 is expressed as a fourth predetermined offset (FoPO), g₄.FoPO g₄ is characterized by a second direction along an axis parallel tothe y′-axis and a fourth magnitude. FoPO g₄ preferably has a magnitudeof 10 nm-100 nm, and more preferably of 15 nm-25 nm. In a preferred,embodiment of the present invention, the magnitude of FoPO g₄ has thesame value as the magnitude of TPO g₃, and the direction of FoPO g₄ is,opposite the direction of TPO g₃.

It is appreciated that, as described hereinabove, the magnitude anddirection of FoPO g₄ characterize the shift between first periodicstructures 376 and second periodic structures 378 when target 310 is ina state of perfect registration. In a typical case, whereinmisregistration between layers 302 and 304 is not equal to zero, theactual shift between first, periodic structures 376 and second periodicstructures 378 is equal to the vector sum of FoPO g₄ and themisregistration.

In the embodiment shown in FIGS. 3A-3G, as seen particularly in FIG. 3B,individual periodic structures of first periodic structures 362 andsecond periodic structures 364 fully or partially overlie each other. Inanother embodiment of the present invention, although the areas in whichfirst periodic structures 362 and second periodic structures 364 areformed overlie each other, the chosen line widths of first periodicstructures 362, line widths of second periodic structures 364, pitch P,pitch Q, FPO g₁ and SPO g₂ may result in individual periodic structuresof first periodic structures 362 and second periodic structures 364alternating in the x′ direction with no overlap between individualperiodic structures. Similarly, in another embodiment of the presentinvention, the chosen line widths of first periodic structures 362, linewidths of second periodic structures 364, pitch P, pitch Q, FPO g₁ andSPO g₂ may result in some of individual periodic structures of firstperiodic structures 362 and second periodic structures 364 fully orpartially overlying each other, and some of individual periodicstructures of first periodic structures 362 and second periodicstructures 364 alternating in the x′ direction with each other.

Similarly, individual periodic structures of first periodic structures366 and second periodic structures 368, first periodic structures 372and second periodic structures 374, and first periodic structures 376and second periodic structures 378 may either overlie or alternate witheach other.

It is appreciated that although target 310, as in the embodiment shownin FIGS. 3A-3G and described hereinabove, includes both x′ targetportion 334 and y′ target portion 354, in another embodiment of thepresent invention, target 310 may include only one of x′ target portion334 and y′ target portion 354. Such a target is useful in themeasurement of misregistration between layers 302 and 304 in the x′direction or y′ direction, respectively.

Reference is now additionally made to FIG. 4, which is a simplifiedillustration of an output signal generated by a portion of target 310when suitably illuminated. It is appreciated that FIG. 4 is illustrativein nature, and is not drawn to scale.

As seen in FIG. 4, an x′ target cell 402, being one of FPPS 312 or SPPS314, generates an output signal 410 upon suitable illumination andmeasurement by a scatterometry misregistration metrology tool. Anexample of a scatterometry misregistration metrology tool useful in themeasurement of target 310 is an ATL™ 100, commercially available fromKLA Corporation of Milpitas, Calif., USA.

Output signal 410 typically includes a desired signal portion 412,generated by positive first-order diffraction of incident radiation byx′ target cell 402, and a desired signal portion 414, generated bynegative first-order diffraction of incident radiation by x′ target cell402.

As is known in the art and described in further detail in U.S. Pat. Nos.9,476,698, 8,330,281 and M. Adel, D. Kandel, V. Levinski, Seligson, A.Kuniaysky, “Diffraction order control in overlay metrology: a review ofthe roadmap options,” Proc. SPIE 6922, Metrology, inspection, andProcess Control for Microlithography XXII, 692202 (14 Mar. 2008), adifference between desired signal portion 412 and desired signal portion414 is a function of misregistration in the x′ direction between layers302 and 304, and the misregistration between layers 302 and 304 in thex′ direction may be calculated from output signal 410. In a preferredembodiment of the present invention, the x′ direction is the same as thedirection as that of semiconductor device axis 306, and themisregistration between layers 302 and 304 in the direction ofsemiconductor device axis 306 may be calculated from output signal 410.

Output signal 410 typically further includes a signal portion 416,generated by 0^(th)-order diffraction of incident radiation by x′ targetcell 402. Associated with each of signal portions 412, 414 and 416 are aplurality of noise portions 430, Noise portions 430 include noiseportions 432, which are generated by diffraction of incident radiationby edges 322 of x′ target cell 302 and noise portions 434, which aregenerated by diffraction of incident radiation by edges 324 of x′ targetcell 402.

As is known in the art, as with all similar structures, edges 322 and324 of x′ target cell 402 diffract incident radiation in a directiongenerally perpendicular to respective edge axes 326 and 328. Thus, noiseportions 432 of output signal 410 propagate generally along a noise axisgenerally perpendicular to edge axis 326 and noise portions 434propagate generally along a noise axis generally perpendicular to edgeaxis 328. As is known in the art, as with all similar periodicstructures, FPPS 312 and SPPS 314 each diffract incident radiation in adirection generally parallel to pitch axis 332. Thus, desired signalportions 412 and 414 of output signal 410 are located along an axis 442,being generally parallel to corresponding pitch axis 332.

Since pitch axis 332 is not perpendicular to either of edge axes 326 or328, when illuminating x′ target cell 402 of target 310 of the presentinvention with suitable incident radiation, the axes along which noiseportions 430, generated by diffraction of incident radiation by edges322 and 324, propagate are not parallel to axis 442 along which desiredsignal portions 412 and 414, diffracted by x′ target cell 402,propagate. Thus, as seen in FIG. 4, the undesired contributions of noiseportions 430 to output signal 410 of target 310 can be readilyidentified and removed, thereby improving the SNR of output signal 410.

In a most preferred embodiment of the present invention, in which pitchaxis 332 forms a generally 45° angle with both of edge axes 326 and 328,the axes along which noise portions 430 propagate are located at, amaximum possible planar radial distance from axis 442 along whichdesired signal portions 412 and 414, diffracted by FPPS 312 and SPPS314, propagate. Thus, the undesired contributions of noise portions 430to output signal 410 can be readily identified and removed, therebyimproving the SNR of output signal 410.

It is appreciated that while FIG. 4 shows output signal 410 for only asingle one of FPPS 312 or SPPS 314, typically both of FPPS 312 and SPPS314 are measured, and output signals 410 from both of FPPS 312 and SPPS314 are analyzed in order to determine both a magnitude and a directionof misregistration in the x′ direction between layers 302 and 304.

It is appreciated that upon suitable illumination and measurement ofeach of TPPS 316 and FoPPS 318 by a scatterometry misregistrationmeasurement tool, an output signal, similar to output signal 410described hereinabove with, reference to FIG. 4, is generated.Typically, the output signal generated by each of TPPS 316 and FoPPS 318is qualitatively identical to an output signal 410 that has been rotatedsuch that axis 442 is parallel to pitch axis 352. Thus, misregistrationin the y′ direction between layers 302 and 304 may be calculated fromthe output signals generated by TPPS 316 and FoPPS 318.

More particularly, each of the output signals generated by TPPS 316 orFoPPS 318 includes desired signal portions of the output signal similarto desired signal portions 412 and 414, which are located along an axisbeing generally parallel to corresponding pitch axis 352. Typically,each of the output signals generated by TPPS 316 or FoPPS 318 furtherinclude noise portions, similar to noise portions 430, which propagatein a different direction than that of axis 352.

Reference is now made to FIG. 5, which is a simplified generally topplanar illustration of another embodiment of a target of the presentinvention, formed on a wafer. It is appreciated that, for ease ofunderstanding, FIG. 5 is not drawn to scale. It is further appreciatedthat in a preferred embodiment of the present invention, at least somefeatures shown may be, and typically are, covered by other structuresalso formed on the wafer.

As seen in FIG. 5, formed on a wafer 500 are at least a first layer 502and a second layer 504. Preferably, first layer 502 and second layer 504include, inter semiconductor device features (not shown), portions ofwhich are generally parallel to either of a semiconductor device axis506 and semiconductor device axis 508. In FIG. 5, semiconductor deviceaxis 506 and semiconductor device axis 508 are shown as perpendicular toeach other, but they need not be.

In one embodiment of the present invention, a target 510 is formedwithin a target-dedicated region 512 on wafer 500. Typically, the sidesof target-dedicated region 512 are generally parallel to one or both ofsemiconductor device axes 506 and 508. In a preferred embodiment of thepresent invention, the size of target 510 is chosen to generallymaximize the ratio of the size of target 510 to the size oftarget-dedicated region 512.

Target 510 preferably includes a scatterometric-sensible portion 520 anda plurality of electron beam-sensitive portions 530. Preferably,scatterometric-sensible portion 520 is identical to target 310, asdescribed hereinabove with reference to FIGS. 3A-4.

As seen in FIG. 5, due to its rotation relative to semiconductor deviceaxes 506 and 508, even in a case wherein scatterometric-sensible portion520 is formed having a maximum possible area that does not extendoutside of target-dedicated region 512, scatterometric-sensible portion520 does not fill the entirety of target-dedicated region 512. In apreferred embodiment of the present invention, electron beam-sensibleportions 530 are formed particularly in those portions oftarget-dedicated region 512 which are not filled byscatterometric-sensible portion 520.

Electron beam sensible portions 530 either alone or together preferablyinclude an assortment of first features 532 formed as part of layer 502and second features 534 formed as part of layer 504, which together forman electron beam target. Such a target may be embodied as, inter alia, atarget such as is shown in FIG. 5, which is similar to targets describedin U.S. Pat. No. 7,608,468 entitled APPARATUS AND METHODS FORDETERMINING OVERLAY AND USES OF SAME.

It is a particular feature of the present invention that preferably,scatterometric-sensible portion 520 and electron beam-sensible portions530 include features formed as part of the same pairs of layers 502 and504. Thus, scatterometric-sensible portion 520 provides an indication ofmisregistration between layers 502 and 504 upon imaging by a suitablescatterometry misregistration measurement tool and electronbeam-sensible portion 530 provides an indication of misregistrationbetween layers 502 and 504 upon imaging by a suitable electron beammisregistration metrology tool.

An example of a scatterometry misregistration metrology tool useful inthe measurement of scatterometric-sensible portion 520 is an ATL™ 100,commercially available from KLA Corporation of Milpitas, Calif., USA. Anexample of an electron beam misregistration metrology tool useful in themeasurement of electron beam-sensible portions 530 is an eDR7380™,commercially available from KLA Corporation of Milpitas, Calif., USA.

In a preferred embodiment of the present invention,scatterometric-sensible portion 520 and electron beam-sensible portions530 are rotationally symmetric about a single point of symmetry 550.Thus, scatterometric-sensible portion 520 and electron beam-sensibleportions 530 each provide an indication of misregistration betweenlayers 502 and 504 at point 550.

The indication of misregistration between layers 502 and 504 provided byscatterometric-sensible portion 520 may be compared to the indication ofmisregistration between layers 502 and 504 provided by electronbeam-sensible portions 530, and a difference between the two indicationsmay be used to calibrate one or both of the misregistration metrologytools used to measure target 510.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. The scope of the present invention includes bothcombinations and subcombinations of various features describedhereinabove as well as modifications thereof, all of which are not inthe prior art.

1. A target for use in the measurement of misregistration between atleast one first layer and at least one second layer formed on a wafer inthe manufacture of semiconductor devices, the target comprising: a firstpair of periodic structures (FPPS) and a second pair of periodicstructures (SPPS), each of said FPPS and said SPPS comprising: a firstedge axis being generally parallel to a first FPPS edge; a second edgeaxis being generally parallel to a second FPPS edge; a plurality offirst periodic structures formed in a first area as part of a first FPPSlayer of said at least one first layer and having a first pitch along afirst pitch axis, said first pitch axis not being parallel to either ofsaid first edge axis or second edge axis; and a plurality of secondperiodic structures formed in a second area as part of a second FPPSlayer of said at least one second layer and having said first pitchalong a second pitch axis: said second pitch axis being generallyparallel to said first pitch axis; and said first area and said secondarea at least partially overlying one another.
 2. The target accordingto claim 1 and also comprising: a third pair of periodic structures(TPPS) and a fourth pair of periodic structures (FoPPS), each of saidTPPS and said FoPPS comprising: a third edge axis being generallyparallel to a first TPPS edge; a fourth edge axis being generallyparallel to a second TPPS edge; a plurality of third periodic structuresformed in a third area as part of a first TPPS layer of said at leastone first layer and having a second pitch along a third pitch axis, saidthird pitch axis not being parallel to either of said third edge axis orfourth edge axis; and a plurality of fourth periodic structures formedin a fourth area as part of a second TPPS layer of said at least onesecond layer and having said second pitch along a fourth pitch axis:said fourth pitch axis being generally parallel to said third pitch axisand said third area; and said fourth area at least partially overlyingone another.
 3. The target according to claim 2 and wherein: said firstFPPS layer and said first TPPS layer are the same layer; and said secondFPPS layer and said second TPPS layer are the same layer.
 4. The targetaccording to claim 2 and wherein at least one of: said first FPPS layerand said first TPPS layer are different layers; and said second FPPSlayer and said second TPPS layer are different layers.
 5. The targetaccording to claim 2 and wherein said third pitch axis is generallyperpendicular to said first pitch axis.
 6. The target according to claim1 and wherein said first pitch axis forms a 45° angle with said firstedge axis.
 7. The target according to claim 1 and wherein said secondedge axis is generally perpendicular to said first edge axis.
 8. Thetarget according to claim 1 and wherein portions of said semiconductordevices are generally parallel to a first semiconductor device axis andsaid first pitch axis is generally perpendicular to said firstsemiconductor device axis.
 9. The target according to claim 8 and alsocomprising electron beam sensible portions comprising: a plurality offirst features formed as part of said at least one first layer of saidwafer; and a plurality of second features formed as part of said atleast one second layer of said wafer.
 10. The target according to claim9 wherein said FPPS, said SPPS and said electron beam sensible portionsare all formed in a single target-dedicated region on said wafer. 11.The target according to claim 9 and wherein said target is rotationallysymmetric about a single point of symmetry.
 12. The target according toclaim 1 and wherein portions of said semiconductor devices are generallyparallel to a first semiconductor axis, and said first pitch axis is notperpendicular to said first semiconductor device axis.
 13. (canceled)14. The target according to claim 12, and wherein said target has afirst size and is formed in a target-dedicated region, saidtarget-dedicated region having a second size, and said target isoriented within said target-dedicated region such that a ratio of saidfirst size to said second size is maximized.
 15. The target according toclaim 1 and wherein said first pitch axis, said first edge axis and saidsecond edge axis are arranged such that when either of said FPPS or saidSPPS is illuminated by light, resulting in: a desired output signalalong a signal axis, said signal axis not being perpendicular to eitherof said first edge axis or said second edge axis; and a noise outputsignal along a first noise axis and a second noise axis, said firstnoise axis being generally perpendicular to said first edge axis andsaid second noise axis being generally perpendicular to said second edgeaxis, wherein overlap between said noise output signal and said desiredoutput signal is minimized.
 16. (canceled)
 17. A method of measuringmisregistration between at least one first layer and at least one secondlayer formed on a wafer in the manufacture of semiconductor devices, themethod comprising: providing said wafer on which is formed a targetcomprising: a first pair of periodic structures (FPPS) and a second pairof periodic structures (SPPS), each of said FPPS and said SPPScomprising: a first edge axis being generally parallel to a first FPPSedge; a second edge axis being generally parallel to a second FPPS edge;a plurality of first periodic structures formed in a first area as partof a first FPPS layer of said at least one first layer and having afirst pitch along a first pitch axis, said first pitch axis not beingparallel to either of said first edge axis or second edge axis; and aplurality of second periodic structures formed in a second area as partof a second FPPS layer of said at least one second layer and having saidfirst pitch along a second pitch axis, said second pitch axis beinggenerally parallel to said first pitch axis and said first area and saidsecond area at least partially overlying one another; illuminating saidtarget with incident radiation, thereby generating output signals; andanalyzing said output signals, thereby generating a misregistrationvalue between said layers of said target.
 18. The method according toclaim 17 and wherein each of said output signals comprises: a desiredoutput signal along a signal axis, said signal axis not beingperpendicular to either of said first edge axis or said second edgeaxis; and a noise output signal along a first noise axis and a secondnoise axis, said first noise axis being generally perpendicular to saidfirst edge axis and said second noise axis being generally perpendicularto said second edge axis, wherein overlap between said noise outputsignal and said desired output signal is minimized.
 19. (canceled) 20.The method according to claim 18 and wherein said analyzing said outputsignals comprises: identifying and removing said noise output signals ofeach of said output signals.
 21. The method according to claim 17 andwherein a scatterometry misregistration metrology tool generates saidoutput signals.
 22. (canceled)
 23. The method according to claim 17 andwherein portions of said semiconductor devices are generally parallel toa first semiconductor device axis and said first pitch axis is generallyperpendicular to said first semiconductor device axis.
 24. The methodaccording to claim 23 and wherein said target also comprises electronbeam sensible portions comprising: a plurality of first features formedas part of said at least one first layer of said wafer; and a pluralityof second features formed as part of said at least one second layer ofsaid wafer.
 25. The method according to claim 24 wherein said FPPS, saidSPPS and said electron beam sensible portions are all formed in a singletarget-dedicated region on said wafer.
 26. The method according to claim24 and wherein said target is rotationally symmetric about a singlepoint of symmetry.
 27. The method according to claim 24 and alsocomprising measuring said electron beam sensible portions using anelectron beam misregistration metrology tool.
 28. The method accordingto claim 17 and wherein portions of said semiconductor devices aregenerally parallel to a first semiconductor axis, and said first pitchaxis is not perpendicular to said first semiconductor device axis. 29.(canceled)